Evolution of pastoralism in Southern Greenland during the last two millennia reconstructed from bile acids and coprophilous fungal spores in lacustrine sediments

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Evolution of pastoralism in Southern Greenland during

the last two millennia reconstructed from bile acids and

coprophilous fungal spores in lacustrine sediments

Typhaine Guillemot, Renata Zocatelli, Vincent Bichet, Jérémy Jacob, Charly

Massa, Claude Le Milbeau, Hervé Richard, Emilie Gauthier

To cite this version:

Accepted Manuscript

Note

Evolution of pastoralism in Southern Greenland during the last two millennia reconstructed from bile acids and coprophilous fungal spores in lacustrine sedi-ments

Typhaine Guillemot, Renata Zocatelli, Vincent Bichet, Jérémy Jacob, Charly Massa, Claude Le Milbeau, Hervé Richard, Emilie Gauthier

PII: S0146-6380(15)00024-8

DOI: http://dx.doi.org/10.1016/j.orggeochem.2015.01.012

Reference: OG 3233

To appear in: Organic Geochemistry Received Date: 30 September 2014 Revised Date: 27 January 2015 Accepted Date: 30 January 2015

Please cite this article as: Guillemot, T., Zocatelli, R., Bichet, V., Jacob, J., Massa, C., Milbeau, C.L., Richard, H., Gauthier, E., Evolution of pastoralism in Southern Greenland during the last two millennia reconstructed from bile acids and coprophilous fungal spores in lacustrine sediments, Organic Geochemistry (2015), doi: http://dx.doi.org/ 10.1016/j.orggeochem.2015.01.012

Evolut ion of past or alism in Sout her n Gr eenland dur ing t he

last t wo millennia r econst r uct ed fr om bile acids and

copr ophilous fungal spor es in lacust r ine sediment s

Typhaine Guillemota,*_{, Renata Zocat elli}b,c,d_{, Vincent Bichet}a_{,Jérémy Jacob}b,c,d_{, Charly}

Massaa

, Claude L e Milbeaub,c,d

,Hervé Richarda

, Emilie Gaut hiera

a

Labor atoir e Chr ono-envir onnement, Univer sité de Fr anche Comté, CNRS UM R 6249, 16 r oute de Gr ay, 25030 Besançon, Fr ance.

b

Univer sité d’Or léans, I STO, UM R, 7327, 45071, Or léans, Fr ance c

CNRS/I NSU, I STO, UM R 7327, 45071, Or léans, France d

BRGM, I STO, UM R 7327, BP 36009, 45060, Or léans, Fr ance *Cor r esponding author .

E mail addr ess: typhaine.guillemot@univ-fcomte.fr (T.Guillemot).

ABSTRACT

To reconstruct the evolution of livestock in SW Greenland over the last two millennia, we measured the concentration of bile acids in a sedimentary sequence retrieved from Lake I galiku. Deoxycholic acid (DOC) was the sole bile acid. and was present throughout the sequence.

Lower DOC and coprophilous fungal spore fluxes values after the Norse abandonment, compared with pre-colonization conditions, could indicate that Norse activit y in conjunction with climate pejoration, altered durably the pristine wildlife.

Therefore, these quantitative correlations between DOC and coprophilous fungal spores fluxes potentially suggest a quantitative relationship with the livestock grazing in the catchment. The comparison between sedimentary DOC and coprophilous fungal spores provides tremendous highlights on past pastoral dynamics over the last 2000 yr in SW Greenland.

Keywords: Greenland, Norse, pastoralism, lake sediments, deoxycholic acid, coprophilous fungal spores.

1. I nt r oduct i on

2. Set t i ng

Lake I galiku [61º00’ N, 45º26’ W, 15 m above sea level (a.s.l)] is a small lake (34.6 ha), with a maximum depth 26 m and catchment area 3.55 km2

.I t is in southwestern Greenland, ca. 1.5 km from the village of I galiku

(Fig. 1). I t has no major inflow but there is a small outflow into the Tunulliarfik fjord. I t is surrounded by relatively low relief and slopes, allowing the establishment of farms, pastures and hay fields (Fig. 1). Southern Greenland has been affected by two phases of agricultural expansion during the last 1700 yr. The first corresponds to the Norse settlement that began in 986 AD and lasted approximately until the middle of the XVt h

century, coincident with the cooling of the Little I ce Age (Dugmore et al., 2012; Massa et al., 2012). The second corresponds to the modern agricultural expansion since 1920, resulting from the desire of the Danish to favour a new introduction of agricultural activities in a favorable climatic context . Nowadays, husbandry in the catchment is limited to two farms established during the 1970s where only sheep are raised (Massa et al., 2012).

3. M at er i al and met hods

Two cores I ga-2007 (130 cm length) and I ga-2011 (87 cm) were retrieved a few m apart under 21 m water depth, using a gravity corer. The age-depth model of I ga-2007 was based on 14 accelerator mass spectrometr y

(AMS) radiocarbon dates and on 210

Pb and 137

applied to I ga-2011 by correlating magnetic susceptibilit y data (measured with a Geotek Multi Sensor Core Logger ) with I ga-2007 (Fig. 2).

Coprophilous fungal spores, particularly Sporormiella spp, were counted in

33 samples spanning the last 1700 yr in Iga-2007, (Gauthier et al., 2010)

and were expressed as flux of number of spores (N/cm2

/an1

) in order to take into account variation in sedimentation rate. Sediment samples (35; 0.5 cm thick) from I ga-2011 were selected for biomarker analysis.

Lipids were extracted from each sample (ca. 2g) using an ASE 200

(Dionex©) with CH₂Cl₂:MeOH (9:1 v/v) at 100 °C and 1000 psi. Considering

the minor mineralogical changes through the core, we did not use recovery standards for the bile acid. I n addition, in-house tests indicated no significant proportion of bound acids, thereby excluding bias due to the proportion of bound vs. free bile acids. The extract was separated into neutral, acidic and polar fractions using solid phase extraction on aminopropyl bonded silica (Jacob et al. 2005). The acid fraction was methylated with anhydrous MeOH /MeCOCl and heating at 55 °C for 1h. After the separation of the fatty acidmethyl esters (eluted with dichloromethane, DCM) from the hydroxy acid methyl esters (eluted with DCM:MeOH 1:1) on activated sil ica; the latter were silylated by reacting

with 100 µl N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) in 200 µl

Thermo-Scientific, Bremen, Germany). The GC instrument was fit ted with a TG-5 MS column (60 m, 0.25 mm, i.d., 0.25 µm film thickness) from Thermo, Bellefonte, PA, USA. Samples were injected at 40 °C (held 1 min) and the oven was programmed to 120 °C at 30 °C/min and then to 300 °C (held 70 min) at 3 °C/min. Each sample was dissolved in toluene and 2µl were injected in splitless mode at 280 °C; the carrier gas was H e at 1.0 ml/min. The MS instrument was operated in the electron ionization (EI ) mode at 70

eV and scanned from m/z 50 to 600. Assignment of bile acids was based on

retention times and mass spectra in literature data (Elhmmali et al., 1997; Tyagi et al., 2008). The concentrations are normalized to total organic

carbon and transformed to fluxes (ng/cm2

/yr) using sedimentation rate and dry density.

4. Resul t s and di scussi on

DOC was the sole bile acid throughout the sequence. From bottom t o top (Fig. 3), before the Norse settlement , DOC flux was low but constant (0.25 ng/cm2

/an). After ca. 1000 AD, it rose to reach a maximum value of

1.77 ng/cm2

/an around ca. 1200 AD, before decreasing to negligible values (< 0.25 ng/cm2

/an) from ca. 1400 to ca. 1930 AD (Fig. 3). From then, the flux increased drastically until reaching values approaching those during the

Norse period (>1.5 ng/cm2

/an). Finally, a slight drop in flux was noted after 2000 AD (Fig. 3).

in faeces (Bull et al., 2002). DOC and other bile acids have been largely studied in water, sewage and surficial estuarine sediments to evaluate faecal pollution and determine its source (Elhmmali et al., 1997; Bull et al., 2002; Tyagi et al., 2008). They have also been studied in anthropogenic and pasture soils (Zocatelli et al., 2012). Bile acids are sparsely reported, however, in ancient environmental samples and were detected in archaeological contexts such as anthropogenic manure palaeosoils (Bull et al., 1999) and Neolithic coprolit es (Shillito et al., 2011). Our results constitute the first evidence of the long term persistence of DOC in lake sediments. The presence of DOC in 1700 yr old samples implies that it did not suffer intensive degradation or leaching and could be more extensively examined in sedimentary archives.

DOC evolution remarkably followed that of Sporormiella spp. spores

(Pearson test; R2

0.6, p_value 0.0005; Fig. 3). Low levels (1 N /cm2

/an) were noted from ca. 300 AD up to ca. 1000 AD, except for a single sample with a higher value (7 N/cm2

/an) at ca. 450 AD that is not an outlier in the DOC data.

Then, as for DOC, Sporormiella flux increased slightly after ca. 1000 AD

and more strongly so after ca. 1100 AD, until reaching a maximum (10

N/cm2

/an) around 1200 AD. After then, Sporormiella flux decreased to 2

N/cm2

/an and remained relatively stable from ca. 1450 to ca. 1920 AD, when

the flux increased rapidly until rising to the highest value of 64 N/cm2

/an.

Thus, both DOC flux and Sporormiella spp. flux were high during the two

was revealed in the catchment (before the Norse colonization and the LI A), with noticeably lower levels after the Norse settlement than before for both tracers.

Coprophilous fungal spores commonly grow on animal dung, especially

of herbivores (Van Geel et al., 2003; Gauthier et al., 2010). Sporormiella spp.

grazing activit y biomarker s (Davis and Shafer 2006). Because their abundance in sediments depends on many factors such as humidity, temperature and competition between species, it is currently difficult to quantitatively relat e their abundance to the intensity of grazing activit y in the catchment (Baker et al., 2013). Similarly, no study has proposed to relate concentration of faecal biomarkers to livest ock size in a catchment. I t is thus remarkable that, except for the most recent sediments, the amplitude of variation in both tracers was comparable. This would suggest that a simil ar quantitative control is exerted on both tracers.

Another striking feature of our record lies in the relatively stable and non -zero levels of DOC and Sporormiella spp. spores before (between ca. 300 AD and ca. 1000 AD) and after (between ca. 1400 and ca. 1900 AD) the Norse

settlement. The background of DOC and Sporormiella spp. spores could

before would suggest a severe reduction in the population of reindeer around I galiku after the Norse period. Such a reduction could result from a combination of (i) direct reduction of the reindeer population by Norse hunting; (ii) reduction in reindeer food resources due to intensive grazing and a diminution in tree and shrub cover (Gauthier et al., 2010) and degradation of soil (an increase in denudation rate is pointed out by Massa et al., 2012); (iii) the climatic deterioration in the LI A. Considering that DOC flux did not return to pre-Norse levels before the Danish recolonization, one could conclude to long term impact of Norse activities on Greenland ecosystems.

5. Concl usions

DOC, a faecal biomarker, was detected in Southern Greenlandic lacustrine sediments dated back to the last two millennia. H igher flux values occurred in sediments deposited during the two phases of livestock breeding in the catchment: the Norse settlement during medieval times and

modern Danish colonization. DOC and Sporormiella spp. spore flux values

Ack nowl edgement s

The research was supported by the University of Franche-Comté, the CNRS, the French Polar I nstitute (I PEV) and the ANR CEP& S “Green Greenland” Project (ANR-10-CEPL-0008). The authors also wish to thank two anonymous reviewers for constructive comments.

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Fi gur e capt i ons

Fi g.1. Location of Lake I galiku: (a) Map of Greenland with study area in the black circle. (b) Focus on region around the lake including paths (dashed lines), buildings (black rectangles), actual hay fields (grey zone) and the archeological site of Gardar. The catchment delimit ation is drawn in dotted lines. (c) Bathymetry of Lake I galiku and core I ga-2011 location.

Fi g.2. Age-depth model for I ga-2007 and correlation between I ga-2007 and

I ga-2011 cores (a) The age-depth model is based on 14

C, 210

Pb and 137

Cs data (dots), according to Massa et al. (2012). (b) Correlation is based on magnetic susceptibility data.

IGA-2007 IGA-2011 0 40 80 120

b)

Age (cal yrs AD)

terrestrial macrofossils

aquatic moss (age reservoir corrected)

137_{Cs and} 210_{Pb model}

0 0.5 1 1.5 2 A ge (y ear AD ) 500 1000 1500 2000 0 5 10 Deoxycholic acid ng.cm-2_.yr-1 Sporormiella N.cm-2_.yr-1 Phase I A gricultur e Phase II Clima te change

Global warming